At the beginning of a brake apply, the fluid displaced out of the master cylinder is used to bring the brake friction material in contact with the brake rotors or drums. This take-up of running clearances is basically lost travel from a pedal feel standpoint. It is desirable to reduce this initial pedal travel and thus to improve pedal feel.
This problem has been recognized in the prior art. For example, U.S. Pat. No. 4,338,787 achieves rapid low force motion of braking members into engagement followed by significantly higher force braking pressure by employing multiple fluid chambers and two dissimilar piston areas, a larger one of which is effective to move fluid and translate the braking members into engagement whereupon a hydraulic valving arrangement causes the master cylinder to transition to using the smaller area piston applying a greater force to the braking surfaces.